The present invention relates to improved spin-on resist and/or thermoplastic material compositions with improved wettabiliiy and adhesion to substrate materials, particularly when utilized with substrate materials utilized in the manufacture of servo-patterned, thin film, hard disk magnetic and/or magneto-optical (MO) recording media, and to an improved method of manufacturing such media.
Spin coating of wafer-shaped substrates or workpieces is a widely utilized process in the manufacture of semiconductor integrated circuit (xe2x80x9cICxe2x80x9d) devices for applying thin, uniform thickness layers of a coating material, e.g., a photoresist, to the wafer surfaces as part of photolithographic patterning of the IC component devices, interconnections, etc., and is increasingly employed as part of the manufacturing process of disk-shaped magnetic and/or magneto-optical (xe2x80x9cMOxe2x80x9d) recording media, such as hard disks, for patterning the surfaces of such media, as for example, in the formation of servo patterns therein by means of imprint lithographic techniques.
A typical horizontally oriented spin coating apparatus according to the conventional art is schematically illustrated in the cross-sectional view of FIG. 1, wherein reference numeral 1 designates a disk-shaped rotatable table or vacuum chuck, supported by a rotatable shaft 2 perpendicular to the plane of table 1, the latter being connected to motor 3 for rotation about a central axis. Wafer W is fixed to the surface of table or vacuum chuck 1 by means of suction ports (not shown in the drawing for simplicity).
Reference numeral 4 indicates a process bowl or cup surrounding rotatable table or vacuum chuck 1, the bottom of which includes at least one exhaust port 5 for removal of superfluous (i.e., excess) resist (or other coating material) which is scattered about during the spin coating process due to centrifugal force; reference numeral 6 indicates a plate or flange for regulating the air currents flowing in the process bowl or cup 4 in order to enhance coating thickness uniformity; and reference numeral 7 indicates an exhaust port for connection to an exhaust source; reference numeral 8 designates a coating material dispensing nozzle, operatively connected via feed tube or conduit 9 to a source S of a coating material, e.g., a photoresist.
In operation of the above-described spin coating apparatus, the coating material, e.g., a photoresist, is dispensed from nozzle 8 of source S onto the surface of wafer W as the wafer is spun by means of rotatable chuck 1. The spinning of the wafer distributes the photoresist over the surface of the wafer and exerts a shearing force that separates excess photoresist from the wafer and evaporates solvent therefrom, thereby providing a thin, smooth, uniform thickness layer of photoresist on the surface of the wafer.
As indicated above, thermal imprint lithography has been recently studied and developed as a low cost alternative technique for fine dimension pattern/feature formation in the surface of a substrate or workpiece, e.g., servo pattern formation in hard disk magnetic and/or magneto-optical (MO) recording media. See, for example, U.S. Pat. Nos. 4,731,155; 5,772,905; 5,817,242; 6,117,344; 6,165,911; 6,168,845 B1; 6,190,929 B1; and 6,228,294 B1, the disclosures of which are incorporated herein by reference. A typical thermal imprint lithographic process for forming nano-dimensioned patterns/features, such as servo patterns in the surface of a thin film magnetic and/or MO recording medium or in the surface of a substrate therefor, is illustrated with reference to the schematic, cross-sectional views of FIGS. 2(A)-2(D).
Referring to FIG. 2(A), shown therein is a mold 10 (also termed a xe2x80x9cstamper/imprinterxe2x80x9d) including a main body 12 having upper and lower opposed surfaces, with a molding (i.e., stamping/imprinting) layer 14 formed on the lower opposed surface. As illustrated, molding layer 14 includes a patterned plurality of features 16 having a desired shape or surface contour, e.g., a servo pattern. A workpiece comprised of a substrate 18 carrying a thin film layer 20 on an upper surface thereof is positioned below, and in facing relation to the molding layer 14. The expression xe2x80x9cworkpiecexe2x80x9d or substrate 18, when utilized herein in the context of manufacture of servo-patterned thin film, hard disk magnetic recording media, refers to a bare non-magnetic substrate for the medium, i.e., without any layers formed thereon, or with one or more layers constituting the medium formed thereon. Thin film layer 20, comprised of a resist or thermoplastic polymeric material, e.g., a poly(methylmethacrylate) (hereinafter xe2x80x9cPMMAxe2x80x9d), is typically formed on the substrate/workpiece surface by a spin coating process such as described supra.
Adverting to FIG. 2(B), shown therein is a compressive molding step, wherein mold 10 is pressed into the thin film layer 20 in the direction shown by arrow 22, so as to form depressed, i.e., compressed, regions 24. In the illustrated embodiment, features 16 of the molding layer 14, e.g., servo pattern features, are not pressed all of the way into the thin film layer 20 and thus do not contact the surface of the underlying substrate 18. However, the top surface portions 24a of thin film 20 may contact depressed surface portions 16a of molding layer 14. As a consequence, the top surface portions 24a substantially conform to the shape of the depressed surface portions 16a, for example, flat. When contact between the depressed surface portions 16a of molding layer 14 and thin film layer 20 occurs, further movement of the molding layer 14 into the thin film layer 20 stops, due to the sudden increase in contact area, leading to a decrease in compressive pressure when the compressive force is constant.
FIG. 2(C) shows the cross-sectional surface contour of the thin film layer 20 following removal of mold 10. The molded, or imprinted, thin film layer 20 includes a plurality of recesses formed at compressed regions 24 which generally conform to the shape or surface contour of features 16 of the molding layer 14. Referring to FIG. 2(D), in a next step, the surface-molded workpiece is subjected to processing to remove the compressed portions 24 of thin film 20 to selectively expose portions 28 of the underlying substrate 18 separated by raised features 26. Selective removal of the compressed portions 24, as well as subsequent selective removal of part of the thickness of substrate 18 (or one or more layers thereon) at the exposed portions 28 thereof, may be accomplished by any appropriate process, e.g., reactive ion etching (RIE) or wet chemical etching.
The above-described imprint lithographic processing is capable of providing submicron-dimensioned features, as by utilizing a mold 10 provided with patterned features 16, e.g., servo pattern features, comprising pillars, holes, trenches, etc., by means of e-beam lithography, RIE, or other appropriate patterning method. Typical depths of features 16 range from about 5 to about 500 nm, depending upon the desired lateral dimension. The material of the molding layer 14 is typically selected to be hard relative to the thin film layer 20, the latter typically comprising a resist or thermoplastic material which is softened when heated. Thus, suitable materials for use as the molding layer 14 include metals, dielectrics, semiconductors, ceramics, and composite materials. Suitable materials for use as thin film layer 20 include resists and thermoplastic polymers, e.g., PMMA, which can be heated to above their glass temperature, Tg, such that the material exhibits low viscosity and enhanced flow.
As indicated above, formation of patterned thin film magnetic and MO recording media, e.g., servo-patterned media, by certain pattern replication methods, particularly replication by means of thermal imprint lithography, involve spin coating a layer of a resist or thermoplastic material on the surface of a suitable non-magnetic substrate, e.g., a glass, ceramic, metal, metallized glass or ceramic substrate, or on the surface of a magnetic or MO medium comprising a laminate of layers on a surface of a non-magnetic substrate. However, inasmuch as the conventionally employed resist formulations are based on the use of organic solvents, such as anisole (methoxybenzene) in the case of PMMA-based resists or thermoplastic polymers, they generally are hydrophobic, leading to poor wettabiliiy and/or adhesion to surfaces of the above-enumerated, generally hydrophilic, non-magnetic substrates for magnetic and MO media, or to magnetic and MO media fabricated thereon. The incompatibility between the generally hydrophobic spun-on resist or thermoplastic material compositions and the generally hydrophilic substrate or media surfaces is manifested in poor wetting of the latter by the former, leading to xe2x80x9cbeadingxe2x80x9d of the resist or thermoplastic material on the disk surface. According to conventional practices, such undesirable xe2x80x9cbeadingxe2x80x9d is overcome either by increasing the quantity of resist or thermoplastic material dispensed by the spin coating apparatus, e.g., by nozzle 8 of source S of the spin coating apparatus of FIG. 1, as by increasing the dispense pressure, or by pre-wetting the substrate with a thin layer of a hydrophilic material, e.g., a layer of water. Either approach, however, is not economically favorable from a large-scale manufacturing viewpoint, in that the cost of the conventionally employed resist or thermoplastic polymer spin-on coating compositions is a significant fraction of the overall manufacturing cost, and pre-wetting increases overall processing time (noting that product yield and throughput are key factors in disk manufacturing technologies). As a consequence, minimization of resist consumption is considered highly desirable in order to maintain economic competitiveness of the above-described thermal imprint lithography process for forming servo patterns in thin film magnetic and/or MO recording media.
In view of the above-described drawbacks and disadvantages inherent in the conventional spin coating methodology for applying a layer of a generally hydrophobic resist or thermoplastic polymeric material, e.g., a PMMA layer, to a generally hydrophilic surface of a substrate, e.g., disk-shaped non-magnetic substrates for magnetic and/or MO recording media (or to the surfaces of disk-shaped magnetic and/or MO recording media), as part of a pattern forming process, there exists a clear need for improved means and methodology for performing spin coating, e.g., resist coating, of generally hydrophilic substrates such as disks for magnetic and/or MO recording media. More specifically, there exists a need for an improved means and methodology for spin coating a generally hydrophilic surface of a substrate with a generally hydrophobic resist or thermoplastic polymeric material, wherein the above-described drawback and disadvantage accruing from the use of incompatible spin coating compositions and substrates is avoided or at least minimized.
The present invention addresses and solves the problems, difficulties, drawbacks, and disadvantages associated with conventional spin coating of a hydrophobic resist composition on a hydrophilic surface of a disk-shaped substrate employed in the manufacture of hard disk magnetic and/or MO recording media, which drawbacks and disadvantages include high resist usage/waste, while maintaining full compatibility with all aspects of conventional automated manufacturing technology for recording media manufacture. Further, the means and methodology afforded by the present invention enjoy diverse utility in spin coating of a variety of materials on a number of different types of substrates and workpieces.
An advantage of the present invention is improved compositions for applying a layer of a resist or thermoplastic material on a hydrophilic surface of a substrate with improved wettability.
Another advantage of the present invention is improved compositions for spin coating a layer of a resist or thermoplastic material on a hydrophilic surface of a substrate for a magnetic or magneto-optical (MO) recording medium, with improved wettability of the surface.
Yet another advantage of the present invention is improved methods for making compositions for applying a layer of a resist or thermoplastic material on a hydrophilic surface of a substrate with improved wettability.
Still another advantage of the present invention is improved methods for making compositions for spin coating a layer of a resist or thermoplastic material on a hydrophilic surface of a substrate for a magnetic or magneto-optical (MO) recording medium, with improved wettability of the surface.
A further advantage of the present invention is an improved method of manufacturing patterned magnetic or magneto-optical (MO) recording media.
A still further advantage of the present invention is an improved method of manufacturing servo patterned magnetic or magneto-optical (MO) recording media, utilizing improved compositions for spin coating a layer of a resist or thermoplastic material on a hydrophilic surface of a substrate for the magnetic or magneto-optical (MO) recording medium, with improved wettability of the surface.
Additional advantages and other aspects and features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a composition for spin coating a layer of a resist or thermoplastic material on a hydrophilic surface of a substrate with improved wettability of the resist or thermoplastic material, comprising:
a resist or thermoplastic material in the form of an ionic complex derived from a precursor resist or thermoplastic material comprising a hydrophobic polymer chain, and
a solvent for the resist or thermoplastic material.
According to embodiments of the present invention, the ionic complex is derived from a precursor resist or thermoplastic material comprising a hydrophobic polymer chain including a plurality of similarly structured, un-ionized pendant groups, wherein the hydrophobic polymer chain is modified to include a major fraction of un-ionized pendant groups and a minor fraction of ionized pendant groups.
In accordance with certain embodiments of the present invention, the resist or thermoplastic material comprises an ionic complex of a poly(methylmethacrylate) (xe2x80x9cPMMAxe2x80x9d) including a hydrophobic polymer chain having a plurality of pendant groups, wherein the major fraction of the pendant groups arc un-ionized ester groups and the minor fraction of the pendant groups are ionized carboxylate (xe2x80x94COOxe2x88x92) groups.
According to particular embodiments of the present invention, each of the ionized pendant groups comprises a carboxylate of a metal cation; and the solvent comprises anisole.
Another aspect of the present invention is a composition for spin coating a layer of a resist or thermoplastic material on a hydrophilic surface of a substrate with improved wettability of the resist or thermoplastic material, comprising:
(a) a resist or thermoplastic material comprising a hydrophobic polymer chain;
(b) an organic solvent for the resist or thermoplastic material; and
(c) a strongly polar organic material soluble in the organic solvent, wherein the proportion by volume of the polar organic material to the organic solvent is sufficiently low as to inhibit precipitation of the resist or thermoplastic material.
According to embodiments of the present invention, the resist or thermoplastic polymer material comprises a PMMA; the organic solvent comprises anisole; and the strongly polar organic material comprises an alcohol, e.g., the strongly polar organic material comprises methanol (CH3OH) or ethanol (C2H5OH).
Still another aspect of the present invention is a method of making a composition for spin coating a layer of a resist or thermoplastic material on a hydrophilic surface of a substrate with improved wettability of the resist or thermoplastic material, comprising steps of:
(a) providing a solution comprised of a precursor resist or thermoplastic material having a hydrophobic polymer chain and an organic solvent; and
(b) forming an ionic complex of the precursor resist or thermoplastic material.
According to embodiments of the present invention, step (a) comprises providing a solution comprised of a precursor resist or thermoplastic material including a hydrophobic polymer chain including a plurality of similarly structured, un-ionized pendant groups; and step (b) comprises modifying the hydrophobic polymer chain of the precursor to include a major fraction of un-ionized pendant groups and a minor fraction of ionized pendant groups.
In accordance with certain embodiments of the present invention, step (a) comprises providing a solution comprised of a precursor resist or thermoplastic material in the form of a PMMA including a polymer chain with a plurality of similarly structured, ester pendant groups; and step (b) comprises modifying the polymer chain to include a major fraction of the ester pendant groups and a minor fraction of ionized carboxylate (xe2x80x94COOxe2x88x92) groups.
According to particular embodiments of the present invention, step (b) comprises introducing an ionic salt or a base to the solution provided in step (a), wherein the amount of ionic salt or base added to the solution is small relative to the amount of precursor resist or thermoplastic material in the solution, whereby only a minor fraction of the ester pendant groups are converted to the ionized carboxylate (xe2x80x94COOxe2x88x92) groups, e.g., as where step (b) comprises introducing K2CO3 as said ionic salt or NaOH or KOH as the base.
Yet another aspect of the present invention is a method of making a composition for spin coating a layer of a resist or thermoplastic material on a hydrophilic surface of a substrate with improved wettability of the resist or thermoplastic material, comprising steps of:
(a) providing a solution comprised of a resist or thermoplastic material having a hydrophobic polymer chain and an organic solvent; and
(b) introducing into the solution a strongly polar organic material in a small amount relative to the amount of the resist or thermoplastic material in the solution, such that precipitation of the resist or thermoplastic material is inhibited.
According to embodiments of the present invention, step (a) comprises providing a solution of a PMMA in anisole; and step (b) comprises introducing an alcohol selected from methanol (CH3OH) or ethanol (C2H5OH) to the solution.
A further aspect of the present invention is a method of manufacturing patterned magnetic or magneto-optical (MO) recording media, comprising steps of:
(a) providing a workpiece including a substrate for a magnetic or magneto-optical (MO) recording medium, the workpiece including at least one major surface of hydrophilic character;
(b) providing a liquid composition comprising a resist or thermoplastic polymer material, the composition adapted for substantially complete wetting of the at least one major surface of the workpiece;
(c) forming a layer of the resist or thermoplastic polymer material on the at least one major surface of the workpiece, comprising applying a thin layer of the liquid composition to the at least one major surface of the workpiece; and
(d) patterning the at least one major surface of said workpiece utilizing the layer of the resist or thermoplastic polymer material.
According to certain embodiments of the present invention, step (d) comprises forming a servo pattern in the at least one major surface of the workpiece.
In accordance with embodiments of the present invention, step (a) comprises providing a workpiece wherein the at least one major surface of hydrophobic character is a bare surface of a substrate for a magnetic or magneto-optical (MO) recording medium or the surface of an uppermost layer of a laminate of layers formed on a substrate for a magnetic or magneto-optical (MO) recording medium; and step (c) comprises applying the thin layer of the liquid composition to the at least one major surface of the workpiece by spin coating.
According to particular embodiments of the present invention, step (b) comprises providing a liquid composition comprising the resist or thermoplastic material in the form of an ionic complex derived from a precursor resist or thermoplastic material comprising a hydrophobic polymer chain, and a solvent for the resist or thermoplastic material, e.g., step (b) comprises providing an ionic complex derived from a precursor resist or thermoplastic material comprising a hydrophobic polymer chain including a plurality of similarly structured, un-ionized pendant groups, wherein the hydrophobic polymer chain is modified to include a major fraction of un-ionized pendant groups and a minor fraction of ionized pendant groups.
In accordance with certain preferred embodiments of the present invention, step (b) comprises providing an ionic complex of a PMMA including a hydrophobic polymer chain having a plurality of pendant groups, wherein the major fraction of the pendant groups are un-ionized ester groups and the minor fraction of the pendant groups are ionized carboxylate (xe2x80x94COOxe2x88x92) groups, and the solvent is anisole.
According to certain other preferred embodiments of the present invention, step (b) comprises providing a liquid composition comprising a resist or thermoplastic material including a hydrophobic polymer chain, an organic solvent for the resist or thermoplastic material, and a strongly polar organic material soluble in the organic solvent, wherein the proportion by volume of the polar organic material to the organic solvent is sufficiently low as to inhibit precipitation of the resist or thermoplastic material, e.g., step (b) comprises providing a liquid composition comprising the resist or thermoplastic material in the form of a solution of a PMMA in anisole as the organic solvent, to which a strongly polar alcohol selected from methanol (CH3OH) or ethanol (C2H5OH) is added.
A still further aspect of the present invention is a composition for spin coating a layer of a resist or thermoplastic material on a hydrophilic surface of a substrate with improved wettability of the resist or thermoplastic material, comprising:
(a) a resist or thermoplastic material comprising a hydrophobic polymer chain or a modified polymer chain; and
(b) means for enhancing the wettability of the resist or thermoplastic material when applied as a layer to a hydrophilic surface.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details susceptible of modification in various obvious respects. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.